I've just installed 10.10 from a minimal iso. I've installed gnome-core and the network manager (among a few other things), and I've added the notification area to the panel.

According to the system monitor, nm-applet is currently running, but I can't see it in the notification area. How can I resolve this?

EDIT:

I've noticed that if I click really close to the right of the notification area I get a nm-applet dropdown box but it says "device not managed" under "Wired Network" (I am connected to the internet though), yet there is no nm-applet graphic.

One of the solutions which hasen't been mentioned here is the work around mentioned in launchpad.

OK, weird, I haven't had this problem for a couple of days now. The thing I did was to right click the panel, select 'properties', and then disable 'expand', wait till the panel resizes and then enable 'expand'

According to your edit, maybe the notification area has been resized so small that it can't show the nmapplet inside it. Try unlocking it and moving it around, or add some other icon to the panel and see if it shows up.